Method and apparatus for depositing tungsten after surface treatment to improve film characteristics

ABSTRACT

A method and system to form a refractory metal layer over a substrate includes introduction of a reductant, such as PH 3  or B 2 H 6 , followed by introduction of a tungsten containing compound, such as WF 6 , to form a tungsten layer. It is believed that the reductant reduces the fluorine content of the tungsten layer while improving the step coverage and resistivity of the tungsten layer. It is believed that the improved characteristics of the tungsten film are attributable to the chemical affinity between the reductants and the tungsten containing compound. The chemical affinity provides better surface mobility of the adsorbed chemical species and better reduction of WF 6  at the nucleation stage of the tungsten layer. The method can further include sequentially introducing a reductant, such as PH 3  or B 2 H 6 , and a tungsten containing compound to deposit a tungsten layer. The formed tungsten layer can be used as a nucleation layer followed by bulk deposition of a tungsten layer utilizing standard CVD techniques. Alternatively, the formed tungsten layer can be used to fill an aperture.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional PatentApplication Serial No. 60/305,765, filed Jul. 16, 2001, which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] Embodiments of the invention relate to the processing ofsemiconductor substrates. More particularly, embodiments of theinvention relate to improvements in the process of depositing refractorymetal layers on semiconductor substrates.

[0004] 2. Description of the Related Art

[0005] The semiconductor processing industry continues to strive forlarger production yields while increasing the uniformity of layersdeposited on substrates having larger surface areas. These same factorsin combination with new materials also provide higher density ofcircuits per unit area of the substrate. As circuit density increases,the need for greater uniformity and process control regarding layerthickness rises. As a result, various technologies have been developedto deposit layers on substrates in a cost-effective manner, whilemaintaining control over the characteristics of the layer. ChemicalVapor Deposition (CVD) is one of the most common deposition processesemployed for depositing layers on a substrate. CVD is a flux-dependentdeposition technique that requires precise control of the substratetemperature and precursors introduced into the processing chamber inorder to produce a desired layer of uniform thickness. Theserequirements become more critical as substrate size increases (e.g.,from 200 mm diameter substrates to 300 mm substrates), creating a needfor more complexity in chamber design and gas flow technique to maintainadequate uniformity.

[0006] A variant of CVD that demonstrates superior step coveragecompared to CVD, is Atomic Layer Deposition (ALD). ALD is based uponAtomic Layer Epitaxy (ALE) that was employed originally to fabricateelectroluminescent displays. ALD employs chemisorption to deposit asaturated monolayer of reactive precursor molecules on a substratesurface. This is achieved by alternatingly pulsing an appropriatereactive precursor into a deposition chamber. Each injection of areactive precursor is separated by an inert gas purge to provide anadsorbed atomic layer to previously deposited layers to form a uniformlayer on the substrate. The cycle is repeated to form the layer to adesired thickness. A drawback with ALD techniques is that the depositionrate is much lower than typical CVD techniques by at least one order ofmagnitude.

[0007] Formation of film layers at a high deposition rate whileproviding adequate step coverage are conflicting characteristics oftennecessitating sacrificing one to obtain the other. This conflict is trueparticularly when refractory metal layers are deposited to coverapertures or vias during formation of contacts that interconnectadjacent metallic layers separated by dielectric layers. Historically,CVD techniques have been employed to deposit conductive material such asrefractory metals in order to inexpensively and quickly fill vias. Dueto the increasing density of semiconductor circuitry, tungsten has beenused based upon superior step coverage to fill these high aspect ratiostructures. As a result, deposition of tungsten employing CVD techniquesenjoys wide application in semiconductor processing due to the highthroughput of the process and good step coverage.

[0008] Depositing tungsten by traditional CVD methods, however, isattendant with several disadvantages. For example, blanket deposition ofa tungsten layer on a semiconductor wafer is time-consuming attemperatures below 400° C. The deposition rate of tungsten may beimproved by increasing the deposition temperature between approximately500° C. to 550° C.; however, temperatures in this higher range maycompromise the structural and operational integrity of the underlyingportions of the integrated circuit being formed. Use of tungsten hasalso complicated photolithography steps during the manufacturing processas it results in a relatively rough surface having a reflectivity of 20%or less than that of a silicon substrate. Finally, tungsten has, provendifficult to deposit uniformly. Variance in film thickness of greaterthan 1% has been shown, thereby causing poor control of the resistivityof the layer. Several prior attempts to overcome the aforementioneddrawbacks have been attempted.

[0009] For example, in U.S. Pat. No. 5,028,565 to Chang et al., which isassigned to the assignee of the present invention, a method is disclosedto improve, inter alia, uniformity of tungsten layers by varying thedeposition chemistry. The method includes, in pertinent part, formationof a nucleation layer over an intermediate barrier layer beforedepositing the tungsten layer via bulk deposition. The nucleation layeris formed from a gaseous mixture of tungsten hexafluoride, hydrogen,silane and argon. The nucleation layer is described as providing a layerof growth sites to promote uniform deposition of a tungsten layerthereon. The benefits provided by the nucleation layer are described asbeing dependent upon the barrier layer present. For example, were thebarrier layer formed from titanium nitride, the tungsten layer'sthickness uniformity is improved as much as 15%. Were the barrier layerformed from sputtered tungsten or sputtered titanium tungsten, thebenefits provided by the nucleation layer are not as pronounced.

[0010] A need exists, therefore, to provide techniques to improve thecharacteristics of refractory metal layers deposited on semiconductorsubstrates.

SUMMARY OF THE INVENTION

[0011] A method and system to form a refractory metal layer over asubstrate includes introduction of a reductant, such as PH₃ or B₂H₆,followed by introduction of a tungsten containing compound, such as WF₆,to form a tungsten layer. It is believed that the reductant reduces thefluorine content of the tungsten layer while improving the step coverageand resistivity of the tungsten layer. It is believed that the improvedcharacteristics of the tungsten film are attributable to the chemicalaffinity between the reductants and the tungsten containing compound.The chemical affinity provides better surface mobility of the adsorbedchemical species and better reduction of WF₆ at the nucleation stage ofthe tungsten layer.

[0012] The method can further include sequentially introducing areductant, such as PH₃ or B₂H₆, and a tungsten containing compound todeposit a tungsten layer. The formed tungsten layer can be used as anucleation layer followed by bulk deposition of a tungsten layerutilizing standard CVD techniques. Alternatively, the formed tungstenlayer can be used to fill an aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a perspective view of one embodiment of a semiconductorprocessing system in accordance with the present invention

[0014]FIG. 2 is a schematic cross-sectional view of one embodiment ofthe processing chambers shown above in FIG. 1.

[0015]FIG. 3 is a schematic cross-sectional view of a substrate showingone possible mechanism of adsorption of a reductant over a substrateduring sequential deposition.

[0016]FIG. 4 is a schematic cross-sectional view of a substrate showingone possible mechanism of adsorption of a refractory metal containingcompound over the substrate after introduction of the reductant.

[0017]FIG. 5 is a graphical representation showing the concentration ofgases present in a processing chamber, such as processing chamber asshown above in FIG. 2.

[0018]FIG. 6 is a graphical representation showing the relationshipbetween the number of ALD cycles and the thickness of a layer formed ona substrate employing sequential deposition techniques, in accordancewith the present invention.

[0019]FIG. 7 is a graphical representation showing the relationshipbetween the number of sequential deposition cycles and the resistivityof a layer formed on a substrate employing sequential depositiontechniques, in accordance with the present invention.

[0020]FIG. 8 is a graphical representation showing the relationshipbetween the deposition rate of a layer formed on a substrate employingsequential deposition techniques and the temperature of the substrate.

[0021]FIG. 9 is a graphical representation showing the relationshipbetween the resistivity of a layer formed on a substrate employingsequential deposition techniques and the temperature of the substrate,in accordance with the present invention.

[0022]FIG. 10 is a schematic cross-sectional view of one embodiment of apatterned substrate having a nucleation layer formed thereon employingsequential deposition techniques, in accordance with the presentinvention.

[0023]FIG. 11 is a schematic cross-sectional view of one embodiment ofthe substrate, shown above in FIG. 10, with a refractory metal layerformed atop of the nucleation layer employing CVD, in accordance withthe present invention.

[0024]FIG. 12 is a graphical representation showing the concentration ofgases present in a processing chamber, such as the processing chamber asshown above in FIG. 2, in accordance with an alternative embodiment ofthe present invention.

[0025]FIG. 13 is a graphical representation showing the concentration ofgases present in a processing chamber, such as processing chamber asshown above in FIG. 2, in accordance with an alternative embodiment ofthe present invention.

[0026]FIG. 14 is a graphical representation showing the fluorine contentversus depth of a refractory metal layer formed on a substrate employingALD, either Ar or N₂ being a carrier gas.

[0027]FIG. 15 is a graphical representation showing the fluorine contentversus depth of a refractory metal layer formed on a substrate employingALD with H₂ being a carrier gas.

[0028]FIG. 16 is a schematic cross-sectional view of one embodiment of asubstrate shown above in FIGS. 3 and 4 upon which a layer of either PH₃or B₂H₆ is disposed between a substrate and a tungsten layer, inaccordance with one embodiment of the present invention.

[0029]FIG. 17 is a graphical representation showing the concentration ofgases present in a processing chamber, such as processing chamber asshown above in FIG. 2, in accordance with one embodiment of the presentinvention.

[0030]FIG. 18 is a schematic cross-sectional view of one embodiment of asubstrate shown above in FIGS. 3 and 4 in which a titanium-containinglayer is deposited between a substrate and a layer of either PH₃ orB₂H₆, in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] Referring to FIG. 1, an exemplary wafer processing systemincludes one or more processing chambers 12 and 14 disposed in a commonwork area 16 surrounded by a wall 18. Processing chambers 12 and 14 arein data communication with a controller 22 that is connected to one ormore monitors, shown as 24 and 26. The monitors typically display commoninformation concerning the process associated with processing chambers12 and 14. One of the monitors 26 is mounted on wall 18, with theremaining monitor 24 being disposed in work area 16. Operational controlof processing chambers 12 and 14 may be achieved by the use of a lightpen, associated with one of the monitors 24 and 26, to communicate withcontroller 22. For example, light pen 28 is associated with monitor 24and facilitates communication with controller 22 through monitor 24.Light pen 39 facilitates communication with controller 22 throughmonitor 26.

[0032] Referring both to FIGS. 1 and 2, each of processing chambers 12and 14 includes a housing 30 having a base wall 32, a cover 34 disposedopposite to base wall 32, and a sidewall 36 extending therebetween.Housing 30 defines a chamber 37, and a pedestal 38 is disposed withinprocessing chamber 37 to support a substrate 42, such as a semiconductorwafer. Pedestal 38 may be mounted to move between cover 34 and base wall32, using a displacement mechanism (not shown), but the position thereofis typically fixed. Supplies of processing gases 39 a, 39 b and 39 c arein fluid communication with processing chamber 37 via a showerhead 40.Regulation of the flow of gases from supplies 39 a, 39 b and 39 c iseffectuated via flow valves 41.

[0033] Depending on the specific process, substrate 42 may be heated toa desired temperature prior to layer deposition via a heater embeddedwithin pedestal 38. For example, pedestal 38 may be resistively heatedby applying an electric current from AC power supply 43 to heaterelement 44. Substrate 42 is, in turn, heated by pedestal 38, and can bemaintained within a desired process temperature range of, for example,about 20° C. to about 750° C. A temperature sensor 46, such as athermocouple, is also embedded in wafer support pedestal 38 to monitorthe temperature of pedestal 38 in a conventional manner. For example,the measured temperature may be used in a feedback loop to control theelectrical current applied to heater element 44 by power supply 43 suchthat the substrate temperature can be maintained or controlled at adesired temperature that is suitable for the particular processapplication. Optionally, pedestal 38 may be heated using radiant heat(not shown). A vacuum pump 48 is used to evacuate processing chamber 37and to help maintain the proper gas flows and pressure inside processingchamber 37.

[0034] Referring to FIGS. 1 and 2, one or both of processing chambers 12and 14, discussed above may operate to deposit refractory metal layerson the substrate employing sequential deposition techniques. One exampleof sequential deposition techniques in accordance with the presentinvention includes atomic layer deposition (ALD). The term “substrate”as used herein includes the substrate, such as semiconductor substratesand glass substrates, as well as layers formed thereover, such asdielectric layers (i.e., SiO₂) and barrier layers (i.e., titanium,titanium nitride and the like).

[0035] Not wishing to be bound by theory, FIG. 3 is a schematiccross-sectional view of a substrate showing one possible mechanism ofadsorption of a reductant over a substrate during sequential deposition.The terms “adsorption” or “adsorb” as used herein are defined to includechemisorption, physisorption, or any attractive and/or bonding forceswhich may be at work and/or which may contribute to the bonding,reaction, adherence, or occupation of a portion of an exposed surface ofa substrate structure. During the sequential deposition technique, inaccordance with the present invention, a batch of a first processinggas, in this case “Aa_(x),” results in a layer of “A” being deposited onsubstrate 42 having a surface of ligand “a” exposed to processingchamber 37. Layer “A” may be a monolayer, more than a monolayer, or lessthan a monolayer. Thereafter, a purge gas enters processing chamber 37to purge gas “Aa_(x),” which has not been incorporated into the layer ofA. FIG. 4 is a schematic cross-sectional view of a substrate showing onepossible mechanism of adsorption of a refractory metal containingcompound over the substrate after introduction of the reductant. Afterpurging gas “Aa_(x)” from processing chamber 37, a second batch ofprocessing gas, “Bb_(y),” is introduced into processing chamber 37. The“a” ligand present on the substrate surface reacts with the “b” ligandand “B” atom, releasing molecules, for example, “ab” and “aA,” whichmove away from substrate 42 and are subsequently pumped from processingchamber 37. In this manner, a surface comprising a layer of B compoundremains upon substrate 42 and exposed to processing chamber 37, shown inFIG. 4. The composition of the layer of B compound may be a monolayer orless of atoms typically formed employing ALD techniques. In otherembodiments, more than a monolayer of B compound may be formed duringeach cycle. Alternatively, the layer of compound B may include a layerof multiple atoms (i.e. other atoms besides atoms of B). In such a case,the first batch and/or the second batch of processing gases may includea mixture of process gases, each of which has atoms that would adhere tosubstrate 42. The process proceeds cycle after cycle, until the desiredthickness is achieved.

[0036] Referring to both FIGS. 3 and 4, although any type of processinggas may be employed, in the present example, the reductant “Aa_(x)” maycomprise B₂H₆ or PH₃ and the refractory metal containing compound,Bb_(y), may comprise WF₆. Some possible reactions are shown below inreference to chemical reaction (1) and chemical reaction (2).

B₂H₆(g)+WF₆(g)→W (s)+2BF₃ (g)   (1)

PH₃ (g)+WF₆ (g)→W (s)+PF₃ (g)   (2)

[0037] Other by-products include but are not limited to H₂, HF, F₂.Other reactions are also possible, such as decomposition reactions. Inother embodiments, other reductants may be used, such as SiH₄.Similarly, in other embodiments, other tungsten containing gases may beused, such as W(CO)₆.

[0038] The purge gas includes Ar, He, N₂, H₂, other suitable gases, andcombinations thereof. One or more purge gas may be used. FIG. 5 is agraphical representation of one embodiment of gases present in aprocessing chamber utilizing two purge gases Ar and N₂. Each of theprocessing gases was flowed into processing chamber 37 with a carriergas, which in this example was one of the purge gases. WF₆ is introducedwith Ar and B₂H₆ is introduced with N₂. It should be understood,however, that the purge gas may differ from the carrier gas, discussedmore fully below. One cycle of the ALD technique in accordance with thepresent invention includes flowing the purge gas, N₂, into processingchamber 37 during time t₁, which is approximately about 0.01 to about 15seconds before B₂H₆ is flowed into processing chamber 37. During timet₂, the processing gas B₂H₆ is flowed into processing chamber 37 for atime in the range of about 0.01 to about 15 seconds, along with acarrier gas, which in this example is N₂. After about 0.01 to about 15seconds have lapsed, the flow of B₂H₆ terminates and the flow of N₂continues during time t₃ for an additional time in the range of about0.01 to about 15 seconds, purging the processing chamber of B₂H₆. Duringtime t₄ which lasts approximately about 0 to about 30 seconds,processing chamber 37 is pumped so as to remove most, if not all, gases.After pumping of process chamber 37, the carrier gas Ar is introducedfor a time in the range of about 0.01 to about 15 seconds during timet₅, after which time the process gas WF₆ is introduced into processingchamber 37, along with the carrier gas Ar during time t₆. The time t₆lasts between about 0.01 to about 15 seconds. The flow of the processinggas WF₆ into processing chamber 37 is terminated approximately about0.01 to about 15 seconds after it commenced. After the flow of WF₆ intoprocessing chamber 37 terminates, the flow of Ar continues for anadditional time in the range of 0.01 to 15 seconds, during time t₇.Thereafter, processing chamber 37 is pumped so as to remove most, if notall, gases therein, during time t₈. As before, time t₈ lastsapproximately about 0 to about 30 seconds, thereby concluding one cycleof the sequential deposition technique, in accordance with the presentinvention. The cycle may be repeated to deposit a tungsten layer to adesired thickness.

[0039] The benefits of employing the sequential deposition technique aremany fold, including flux-independence of layer formation that providesuniformity of deposition independent of the size of a substrate. Forexample, the measured difference of the layer uniformity and thicknessmeasured between a 200 mm substrate and a 300 mm substrate deposited inthe same chamber is negligible. This is due to the self-limitingcharacteristics of the sequential deposition techniques. Further, thistechnique contributes to improved step coverage over complex topography.

[0040] In addition, the thickness of the layer B, shown in FIG. 4, maybe easily controlled while minimizing the resistance of the same byemploying sequential deposition techniques. With reference to FIG. 6, itis seen in the slope of line 50 that the thickness of the tungsten layerB is proportional to the number of cycles employed to form the same. Theresistivity of the tungsten layer, however, is relatively independent ofthe thickness of the layer, as shown by the slope of line 52 in FIG. 7.Thus, employing sequential deposition techniques, the thickness of arefractory metal layer maybe easily controlled as a function of thecycling of the process gases introduced into the processing chamber witha negligible effect on the resistivity.

[0041]FIG. 8 is a graphical representation showing the relationshipbetween the deposition rate of a layer formed on a substrate employingsequential deposition techniques and the temperature of the substrate.Control of the deposition rate was found to be dependent upon thetemperature of substrate 42. As shown by the slope of line 54,increasing the temperature of substrate 42 increased the deposition rateof the tungsten layer B. The graph shows that less than a monolayer, amonolayer, or more than a monolayer of a tungsten layer may be formeddepending on the substrate temperature utilized. For example, at 56, thedeposition rate is shown to be approximately 2 Å/cycle at 250° C.However at point 58 the deposition rate is approximately 5 Å/cycle at atemperate of 450° C. The resistivity of the tungsten layer, however, isvirtually independent of the layer thickness, as shown by the slope ofcurve 59, shown in FIG. 9. As a result, the deposition rate of thetungsten layer may be controlled as a function of temperature withoutcompromising the resistivity of the same. However, it may be desirableto reduce the time necessary to deposit an entire layer of a refractorymetal.

[0042] To that end, a bulk deposition of the refractory metal layer maybe included in the deposition process. Typically, the bulk deposition ofthe refractory metal occurs after the nucleation layer is formed in acommon processing chamber. Specifically, in the present example,nucleation of a tungsten layer occurs in chamber 12 employing thesequential deposition techniques discussed above, with substrate 42being heated in the range of about 200° C. to about 400° C., andprocessing chamber 37 being pressurized in the range of about 1 to about10 Torr. A nucleation layer 60 of approximately about 120 to about 200 Åis formed on a patterned substrate 42, shown in FIG. 10. Nucleationlayers of about 100 Å or less, about 50 Å or less, or about 25 Å or lesshave also been found to be effective in providing good step coverageover apertures having an aspect ratio of about 6:1 or greater. As shown,substrate 42 includes a barrier layer 61 and a patterned layer having aplurality of vias 63. The nucleation layer is formed adjacent to thepatterned layer covering vias 63. As shown, forming nucleation layer 60employing ALD techniques provides good step coverage. In anotherembodiment, sequential deposition techniques may be performed for bothnucleation and bulk deposition. In still another embodiment, to decreasethe time required to form a complete layer of tungsten, a bulkdeposition of tungsten onto nucleation layer 60 occurs using CVDtechniques, while substrate 42 is disposed in the same processingchamber 12, shown in FIG. 1. The bulk deposition may be performed usingrecipes well known in the art. In this manner, a tungsten layer 65providing a complete plug fill is achieved on the patterned layer withvias having aspect ratios of approximately 6:1, shown in FIG. 11.

[0043] In an alternative embodiment, a bifurcated deposition process maybe practiced in which nucleation of the refractory metal layer occurs ina chamber that is different from the chamber in which the remainingportion of the refractory metal layer is formed. Specifically, in thepresent example, nucleation of a tungsten layer occurs in chamber 12employing the sequential deposition techniques, such as ALD, discussedabove. To that end, substrate 42 is heated in the range of about 200° C.to about 400° C. and chamber 37 is pressurized in the range of about 1to about 10 Torr. A nucleation layer 60 of approximately 120 to 200 Å isformed on a patterned substrate 42, shown in FIG. 10. Nucleation layersof about 100 Å or less, about 50 Å or less, or about 25 Å or less havealso been found to be effective in providing good step coverage overapertures having an aspect ratio of about 6:1 or greater. As shown,substrate 42 includes a barrier layer 61 and a patterned layer having aplurality of vias 63. The nucleation layer is formed adjacent to thepatterned layer covering the vias 63. As shown, forming the nucleationlayer 60 employing sequential deposition techniques provides improvedstep coverage.

[0044] In one embodiment, sequential deposition techniques are employedfor bulk deposition of tungsten onto nucleation layer 60 occurs whilesubstrate 42 is disposed in processing chamber 14, shown in FIG. 1. Thebulk deposition maybe performed using recipes disclosed herein. Inanother embodiment, CVD techniques are employed for bulk deposition oftungsten onto nucleation layer 60 occurs while substrate 42 is disposedin processing chamber 14, shown in FIG. 1. The bulk deposition maybeperformed using recipes well known in the art. Whether sequentialdeposition or CVD deposition techniques are employed, a tungsten layer65 providing a complete plug fill is achieved on the patterned layerwith vias having aspect ratios of approximately 6:1, shown in FIG. 11.Implementing the bifurcated deposition process discussed above maydecrease the time required to form a tungsten layer having improvedcharacteristics. Utilizing CVD deposition techniques for bulk depositionmay further increase throughput.

[0045] As mentioned above, in an alternate embodiment of the presentinvention, the carrier gas may differ from the purge gas, as shown inFIG. 12. The purge gas, which is introduced at time intervals t₁, t₃, t₅and t₇ comprises Ar. The carrier gas, which is introduced at timeintervals t₂ and t₆, comprises of N₂. Thus, at time interval t₂ thegases introduced into the processing chamber include a mixture of B₂H₆and N₂, and a time interval t₆, the gas mixture includes WF₆ and N₂. Thepump process during time intervals t₄ and t₈ is identical to the pumpprocess discussed above with respect to FIG. 5. In yet anotherembodiment, shown in FIG. 13, the carrier gas during time intervals t₂and t₆ comprises H₂, with the purge gas introduced at time intervals t₁,t₃, t₅ and t₇ comprising of Ar. The pump processes at time intervals t₄and t₈ are as discussed above, As a result, at time interval t₂ the gasmixture introduced into processing chamber 37 comprises of B₂H₆ and H₂,and WF₆, and H₂ at time interval t₆.

[0046] An advantage realized by employing the H₂ carrier gas is that thestability of the tungsten layer B may be improved. Specifically, bycomparing curve 66 in FIG. 14 with curve 68 in FIG. 15, it is seen thatthe concentration of fluorine in the nucleation layer 60, shown in FIG.10, is much less when H₂ is employed as the carrier gas, as comparedwith use of N₂ or Ar as a carrier gas.

[0047] Referring to both FIGS. 14 and 15, the apex and nadir of curve 66show that the fluorine concentration reaches levels in excess of 1×10²¹atoms per cubic centimeter and only as low as just below 1×10¹⁹ atomsper cubic centimeter. Curve 68, however, shows that the fluorineconcentration is well below 1×10²¹ atoms per cubic centimeter at theapex and well below 1×10¹⁷ atoms per cubic centimeter at the nadir.Thus, employing H₂ as the carrier gas provides a much more stable film,i.e., the probability of fluorine diffusing into the substrate, oradjacent layer is reduced. This also reduces the resistance of therefractory metal layer by avoiding the formation of a metal fluoridethat may result from the increased fluorine concentration. Thus, thestability of the nucleation layer, as well as the resistivity of thesame, may be controlled as a function of the carrier gas employed. Thisis also true when a refractory metal layer is deposited entirelyemploying ALD techniques, i.e., without using other depositiontechniques, such as CVD.

[0048] In addition, adsorbing a layer 70, shown in FIG. 16, of eitherPH₃ or B₂H₆ prior to introduction of the tungsten containing compoundforms a tungsten layer 72 with reduced fluorine content, improved stepcoverage, and improved resistivity. This was found to be the case wherethe tungsten containing compound is introduced over a layer of PH₃ orB₂H₆ employing sequential deposition techniques or employing standardCVD techniques using either tungsten hexafluoride, WF₆, and silane,SiH₄, or tungsten hexafluoride, WF₆, and molecular hydrogen, H₂,chemistries. The improved characteristics of the tungsten film arebelieved to be attributable to the chemical affinity between the PH₃ orB₂H₆ layer and the WF₆ layer. This provides better surface mobility ofthe adsorbed chemical species and better reduction of WF₆ at thenucleation stage of the tungsten layer. This has proven beneficial whendepositing a tungsten layer adjacent to a titanium containing adhesionlayer formed from titanium, Ti, or titanium nitride, TiN. Layer 70 ispreferably a monolayer, but in other embodiments may be less than ormore than a monolayer. Layer 70 in the film stack, shown in FIG. 16,shows the formation of the tungsten layer 72. It is understood thatlayer 70 may or may not be consumed during formation of the tungstenlayer 72. It is also understood that a plurality of layers 70 andtungsten layers 72 may be deposited to form a tungsten layer to adesired thickness. As shown, layer 70 is deposited on substrate 74 thatincludes a wafer 76 that may be formed from any material suitable forsemiconductor processing, such as silicon. One or more layers, shown aslayer 74, may be present on wafer 76. Layer 78 may be formed from anysuitable material, included dielectric or conductive materials. Layer 78includes a void 80, exposing a region 82 of wafer 76.

[0049]FIG. 18 is a detailed cross-sectional view of a substrate in whicha titanium-containing adhesion layer is formed between a substrate and alayer of either PH₃ or B₂H₆ during the fabrication of a W layer adjacentto the titanium-containing adhesion layer. The titanium-containingadhesion layer may be formed employing standard CVD techniques. In oneembodiment, the titanium-containing adhesion layer is formed employingsequential deposition techniques. To that end, processing gas Aa_(x) isselected from the group including H₂, B₂H₆, SiH₄ and NH₃. Processing gasBb_(y) is a titanium-containing gas selected from the group thatincludes TDMAT, TDEAT and TiCl₄. Also, Ar and N₂ purge gases arepreferably employed, although other purge gas may be used.

[0050] Referring to FIGS. 2 and 17, each of the processing gases isflowed into processing chamber 37 with a carrier gas, which in thisexample, is one of the purge gases. It should be understood, however,that the purge gas may differ from the carrier gas, discussed more fullybelow. One cycle of the sequential deposition technique, in accordancewith the present invention, includes flowing a purge gas into processingchamber 37 during time t₁ before the titanium-containing gas is flowedinto processing chamber 37. During time t₂, the titanium-containingprocessing gas is flowed into the processing chamber 37, along with acarrier gas. After t₂ has lapsed, the flow of titanium-containing gasterminates and the flow of the carrier gas continues during time t₃,purging the processing chamber of the titanium-containing processinggas. During time t₄, the processing chamber 37 is pumped so as to removeall gases. After pumping of process chamber 37, a carrier gas isintroduced during time t₅, after which time the reducing process gas isintroduced into the processing chamber 37 along with the carrier gas,during time t₆. The flow of the reducing process gas into processingchamber 37 is subsequently terminated. After the flow of reducingprocess gas into processing chamber 37 terminates, the flow of carriergas continues, during time t₇. Thereafter, processing chamber 37 ispumped so as to remove all gases therein, during time t₈, therebyconcluding one cycle of the sequential deposition technique inaccordance with the present invention. The aforementioned cycle isrepeated multiple times until titanium-containing layer reaches adesired thickness. For example, in reference to FIG. 18, after TiN layer84 reaches a desired thickness, layer 86, in this example formed fromPH₃ or B₂H₆, is deposited adjacent thereto employing sequentialdeposition techniques, as discussed above. Thereafter, a layer oftungsten 88, shown in FIG. 18, is disposed adjacent to layer 86 usingthe sequential deposition technique or standard CVD techniques, both ofwhich are discussed above. Layer 86 is preferably a monolayer, but inother embodiments may be less than or more than a monolayer. Layer 86 inthe film stack, shown in FIG. 18, shows the formation of the tungstenlayer 88. It is understood that layer 86 may or may not be consumedduring formation of the tungsten layer 88. It is also understood that aplurality of layers 86 and tungsten layers 66 may be deposited to form atungsten layer to a desired thickness. If desired, a copper layer maybedeposited atop of tungsten layer 88. In this manner, tungsten mayfunction as a barrier layer.

[0051] Referring again to FIG. 2, the process for depositing thetungsten layer may be controlled using a computer program product thatis executed by controller 22. To that end, controller 22 includes acentral processing unit (CPU) 90, a volatile memory, such as a randomaccess memory (RAM) 92 and permanent storage media, such as a floppydisk drive for use with a floppy diskette, or hard disk drive 94. Thecomputer program code can be written in any conventional computerreadable programming language; for example, 68000 assembly language, C,C++, Pascal, Fortran and the like. Suitable program code is entered intoa single file, or multiple files, using a conventional text editor andstored or embodied in a computer-readable medium, such as hard diskdrive 94. If the entered code text is in a high level language, the codeis compiled and the resultant compiler code is then linked with anobject code of precompiled Windows® library routines. To execute thelinked and compiled object code, the system user invokes the objectcode, causing the CPU 90 to load the code in RAM 92. The CPU 90 thenreads and executes the code to perform the tasks identified in theprogram.

[0052] Although the invention has been described in terms of specificembodiments, one skilled in the art will recognize that various changesto the reaction conditions, i.e., temperature, pressure, film thicknessand the like can be substituted and are meant to be included herein.Additionally, while the bifurcated deposition process has been describedas occurring in a common system, the bulk deposition may occur in aprocessing chamber of a mainframe deposition system that is differentfrom the mainframe deposition system in which the processing chamber islocated that is employed to deposit the nucleation layer. Finally, otherrefractory metals may be deposited, in addition to tungsten, and otherdeposition techniques may be employed in lieu of CVD. For example,physical vapor deposition (PVD) techniques, or a combination of both CVDand PVD techniques may be employed. The scope of the invention shouldnot be based upon the foregoing description. Rather, the scope of theinvention should be determined based upon the claims recited herein,including the full scope of equivalents thereof.

1. A method of sequential deposition of a tungsten nucleation layer overa substrate in a processing chamber, comprising: introducing a reductantselected from a group including of PH₃ and B₂H₆, and introducing atungsten containing compound.
 2. The method of claim 1, wherein thenucleation layer is formed over a titanium-containing layer.
 3. Themethod of claim 1, wherein a bulk tungsten layer is formed over thenucleation layer.
 4. The method of claim 3, wherein the bulk tungstenlayer is formed by sequential deposition.
 5. The method of claim 3,wherein the bulk tungsten layer is formed by chemical vapor deposition.6. The method of claim 3, wherein the bulk tungsten layer is formed byphysical vapor deposition.
 7. The method of claim 3, wherein thenucleation layer and the bulk tungsten layer are formed in a commonprocessing chamber.
 8. The method of claim 3, wherein the nucleationlayer and the bulk tungsten layer are formed in separate processingchambers.
 9. The method of claim 2, wherein the titanium-containinglayer and the nucleation layer are formed in separate processingchambers.
 10. A method of depositing a tungsten layer over a substratein a processing chamber, comprising: adsorbing a layer over thesubstrate comprising a compound selected from a group including of PH₃and B₂H₆; and introducing a tungsten containing compound to form atungsten layer.
 11. The method of claim 10, wherein introducing atungsten containing compound comprises introducing a tungsten containingcompound in a sequential deposition technique.
 12. The method of claim10, wherein introducing a tungsten containing compound comprisingintroducing a tungsten containing compound in a chemical vapordeposition technique.
 13. The method of claim 10, wherein the adsorbedlayer is formed over a titanium containing layer.
 14. The method ofclaim 10, wherein adsorbing a layer and introducing a tungstencontaining compound are performed in a common processing chamber. 15.The method of claim 10, wherein adsorbing a layer and introducing atungsten containing compound are performed in separate processingchambers.
 16. A processing system for a substrate, comprising: a bodydefining a processing chamber; a holder disposed within the processingchamber to support the substrate; a gas delivery system in fluidcommunication with the processing chamber; a controller in electricalcommunication with the gas delivery system; and a memory in datacommunication with the controller, the memory comprising acomputer-readable medium having a computer-readable program embodiedtherein, the computer-readable program including a set of instructionsfor introducing a reductant selected from a group including of PH₃ andB₂H₆ and introducing a tungsten containing compound to form a nucleationlayer.
 17. The processing system of claim 16, wherein thecomputer-readable program includes a second set of instructions to forma bulk tungsten layer over the nucleation layer.
 18. The processingsystem of claim 16, further comprising: a second body defining a secondprocessing chamber; wherein the controller is in electricalcommunication with the second body; and wherein the second set ofinstructions control formation of the bulk tungsten layer in the secondbody.